There are wireless sensor network systems as the above type of network systems. In a wireless sensor network system, on generating a path with a sink node as the destination and a sensor node as the source by applying a routing protocol suitable for wireless multihop networks such as OLSR (Optimized Link State Routing), AODV (Ad hoc On-Demand Distance Vector), and the like, as a result, a network topology of tree structure (to be referred to as tree topology hereinbelow) is constructed with a sink node as the apex and sensor nodes positioned at the portions of knots and leaves. In this case, however, bias may occur in the number of child nodes among a plurality of nodes of the same hierarchy. Since such kind of bias causes an increase of load on specific nodes, it is necessary to remove it as far as possible.
The following Patent Document 1 discloses an example of the path control method for removing such bias occurring in the tree topology as described above. In this technique, if a specific device (the network construction device 30 in FIG. 1 of the Patent Document 1) detects that a bias is occurring in the generated tree topology, in order to remove the bias, the system analyzes between which nodes connection should be changed, and carries out connection change after sending a message to each of the nodes as the objects of connection change.
[Patent Document 1] JP 2010-166150 A
However, in the method for carrying out connection change after sending a message to each node of a connection change object, it is necessary to interchange messages of transmission and response in proportion to the node number of the connection change objects.